1. Field of the Invention
The present invention relates to an image processing apparatus for detecting lane marks, vehicles, or the like by processing an image of the road ahead captured by an onboard video camera mounted in a suitable position such as the position of the rearview mirror.
2. Description of the Related Art
A video camera mounted in a vehicle captures an image of the road ahead of or behind the vehicle, and an image processing apparatus processes the captured image data and detects vehicles, white lines, etc. on the road ahead to control vehicle-to-vehicle distance, etc.
Such an image processing apparatus can be used to issue an audible alarm to the driver when the distance to the vehicle ahead has been reduced below a preset value, or when the vehicle the driver is driving begins to run over a lane mark.
The image processing apparatus can be used not only to monitor objects ahead when the vehicle is moving forward, but also to detect obstacles in the rear when the vehicle is moving backward.
Thus, the image processing apparatus has the function of capturing the road condition, such as lane marks and other vehicles, in the form of an image and of recognizing the road condition by processing the image. That is, the apparatus performs the function of image recognition.
FIG. 1 is an example of an image captured by a video camera. This image consists of 480 pixels vertically and 640 pixels horizontally, that is, the pixel count is 480×640=307,200. Since each pixel is represented by 8 bits, the data bit count is307,200×8=2,457,600That is, the amount of data exceeds 2M bits.
For image processing, the data obtained from the video camera is temporarily stored in a memory, and the stored data is processed to obtain necessary information.
Of the component elements of the image processing apparatus, the cost of the memory is by no means small compared with the total cost of the apparatus. The cost of the memory is generally proportional to the capacity of the memory. In the above image processing apparatus, since the amount of data obtained by A/D converting the image signal supplied from the video camera is very large, the memory capacity needed also becomes large, making it difficult to reduce the cost of the memory (a first problem).
There is also the following problem, which is associated with the video camera forming part of the image processing apparatus. That is, there inherently occurs an optical axis misalignment in the stereo camera constituting the video camera. To correct this optical axis misalignment, it has previously been practiced to correct it manually by measuring the amount of optical axis misalignment by using a test pattern at the factory prior to shipment. This method has been impractical as it takes an enormous amount of time and labor. To address this, it is practiced to input the amount of optical axis misalignment to the CPU and have the CPU perform operations to add or subtract the amount of optical axis misalignment to or from the position data, for example, on the image surface of a vehicle traveling ahead. This, however, imposes a greater burden on the CPU, and the image processing speed becomes slow (a second problem).